No. Just no. While genetically speaking I don't see a problem with it its kinda creepy. Imagine getting married and only your family is supposed to show up. I'd find it far less creepy if people met randomly and didn't know the connection. But if you meet at a family reunion or event its kinda creeping and would gross me out.

Personally, I wouldn't even think about it. Not even if said third cousin was extremely attractive.

How about the rest of Crunchyroll?

Third cousin: The grandchildren of two first cousins; also the children of two second cousins (your parent's cousins).Never the first case, maybe the second.....If I was desperate. I do have a relative who's my cousin twice. I try not to think about it.